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Volume 4 - 3
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  3. African Origins By Professor Phillip V. Tobias The biggest shake-up in the history of our understanding of human evolution occurred here in South Africa, eighty years ago. Against prevailing expectations, that had set human origins in eastern and southeastern Asia, a skull was brought to light in the Buxton Limeworks, Taung, north of Kimberley. That discovery, which reached the desk of Raymond Dart, Professor of Anatomy at the Witwatersrand University Medical School, was destined to upset the paradigms of its day. The child skull of Taung was in due course to overthrow the paradigm that humanity had arisen from Asian roots and replace it with a new and revolutionary paradigm - namely, that humanity had arisen in Africa. Eighty years of further discoveries in South, East and Central Africa have strengthened the paradigm. The “new” paradigm which was put forward in 1925 is now widely accepted by virtually all investigators. Africa is the home of mankind's early ancestors. Since all living mankind has stemmed from those ancient African roots, it is no exaggeration to proclaim, “We are all Africans!” Two other paradigms that have held sway for many years have recently been overthrown. One referred to dating when the human line of descent first emerged on our planet. The other had to do with the environmental conditions, the ecology within which early hominids came to stand, walk and run in an upright position on two legs, as we humans do today. To take the second one first: Ever since the twentieth century discoveries by Professor Dart and Dr Robert Broom of ape-men in South Africa, it has been a widely-held belief that our ancestors came upright and assumed the bipedal stance and gait under savanna conditions, that is open, grass-covered veld, interspersed with light woodland. Most people have held to this Savanna Hypothesis for the last 75 years. Then, within the last decade or so, it was found that South and East African hominids (or members of the family of mankind) were living in well-wooded and even forested conditions. The evidence for this change came from fossil plants and animals that were contemporaries of the early hominids. The Savanna Hypothesis was no longer tenable. Another important paradigm has been overthrown since the beginning of the twenty-first century. In 2001, the paradigm that hominids appeared on earth between five and seven million years ago was proved invalid. This hypothesis had been based on the study of molecules. Molecular dating of fossils was introduced in the second half of the twentieth century and it proved to be one of the most valuable developments for the dating of the past. For a quarter of a century, five to seven million years had been accepted as the most probable time for the separation of the human lineage from that of the chimpanzee. In order to establish what habitat coelacanths prefer in order to predict where more populations might be found, one of the first tasks undertaken by Acep was to map the canyons in which coelacanths occur. When the molecular dating method came into the picture, it was no longer enough to delve into the evolution of life with a pick and shovel, a hammer and chisel. The molecules provided a wonderful new method for probing the past. It was such probings that led, about thirty years ago, to the idea that hominids and proto-chimps had moved apart from one another about five to seven millions of years ago. Since that time, five-to-seven has stood as the most widely accepted estimate of the divergence time. The five-to-seven paradigm was then seriously questioned from two different lines of evidence. Fossil bones were recovered from Ethiopia and Kenya which were claimed to be hominid, and which were older than the spellbinding 5.0 million years. In Ethiopia, Yohannes Haile-Selassie recovered hominid fossils west of the Awash River. What was so spinechilling about this claimed hominid was that it was dated to between 5.2 and 5.8 million years ago. In April 2002, some even older specimens were found in the Tugen Hills of central Kenya. The French and Kenyan discoverers concluded from their study of the thigh-bone (femur) that the creature was a biped and that this was the earliest bipedal hominid. While not everyone agrees with this, the dating is not in doubt: It is about 6.0 million years ago. Then, from the Chad Republic, 2,500 kms west of Africa's Great Rift Valley, a French and Chadian team found a set of remains whose anatomy pointed to their being hominid. What was so shocking was the date claimed: The deposit from which they emanated was between six and seven million years old. If all these new remains were definitely hominid, this would mean that hominids were in existence already by seven million years. The five-to-seven paradigm had also to be thrown out of the window. By a remarkable coincidence or synchronicity, at the time when these new, earlier supposed hominids were coming to light, molecular biologists at Lund in Sweden were mounting a molecular challenge to the five-toseven paradigm. They had produced reason to query the calibration of the molecular clock. The initial calibration had been based on a kick-off point that was obtained from the fossil record. The discovery of new specimens of well-dated, very ancient mammals made them realise that the clock had been incorrectly calibrated. They re-calibrated the clock, making use of newly excavated kick-off points and came up with new estimates for the origin of the hominids. Instead of five to seven million years, they estimated 10.5 to 13.0 million years that is, approximately twice as ancient. From the new molecular estimates, made quite independently of the recent Ethiopian, Kenyan and Chadian hominid discoveries, it is likely now that the first hominids to appear on our planet dwelt in mid-Miocene times (the Miocene is dated to 5-22 million years ago). It follows that the diversification of modern humans goes back earlier than the 100,000 to 200,000 years before the present that has been accepted for decades. The new estimates based on the re-calibrated clock would push the diversification of modern humanity to almost half a million years ago.  Correlations between coelacanth behaviour
and changes in the physical environment will define the sensitivity of
coelacanths to such features and enable predictions to be made
regarding vulnerability to change. These in turn have consequences for
conservation and management. Acep plans to attach miniature electronic
acoustic transmitter tags to several coelacanths. Each transmitter has
a unique acoustic code and transmits its depth over specified time
intervals, using an omni-directional signal that covers 600 metres. An
array of acoustic ‘listening receivers’ (data-loggers), set up at
distances of 500 to 700 metres, collect and store the transmitted
data.A glimpse of the breccia or cave deposit at Sterkfontein. “Mrs. Ples” was found near the edge of the right hand pit. The point of all this is that the relatively recent period of human race formation is much smaller than the period spent by each population in common with all other races. Only about five percent of the time of hominids on earth has been spent in this recent period of diversification. That is to say, humankind shares far more of its genome in common with one another, than that part of the genome that distinguishes one human population from another. While the newly-recovered most ancient hominids have come from East and Central Africa, the dating of the oldest hominids so far recovered in South Africa is not as old. Until recently, the oldest South African datings were for ape-man remains from Mokopane (Makapansgat) in the Limpopo Province: these were dated to 3.2 million years. The astonishing, virtually complete hominid skeleton found in one of the deepest strata in the Sterkfontein caves, which we formerly dated to some 3.3 million years, has recently been re-dated by the first-time application in Africa of a new method for dating based on buried cosmogenic nuclides. This yields a dating for that skeleton of 4.2 million years ago, making it the oldest dated hominid specimen found in southern Africa. Dating, is not everything, however. While the East and Central African sites are all open-air localities near rivers or lakes, with many scattering factors in the environment, South Africa's oldest sites are all in dolomitic, limestone caves. These sealed cave deposits protect the ancient remains remarkably well, so that from Sterkfontein we have over 700 apeman remnants and from Swartkrans some 300.  This skull, the type specimen of
Australopithecus africanus, was discovered in the Buxton Limeworks at
Taung in South Africa late in 1924. It was recognised as representing a
new kind of higher primate by R.A. Dart (1925). Save for the first
permanent molars, all of the erupted teeth are deciduous. By modern
standards, the individual to whom this skull belonged would have been
between 3 and 4 years of age at death. This was the first of Africa’s
ape-man or australopithecine fossils to be found and Dart’s recognition
of its hominid features constituted one of the most important events in
the history of palaeo-anthropology in the 20th Century. [Photo: A.R.
Hughes] male and female, young and old, individual variants and the amount of variation within a single species. We can assess such variability better than from any of the East African open sites, where there is more possibility for dismembering, scattering and mixing of different kinds of ape-men. Another advantage of our cave fossil deposits is that, in Sterkfontein, we have so far obtained no fewer than four partial skeletons of early hominids. It is quite exceptional, at these depths in time, to find even a single partial hominid skeleton. Even if South Africa does not have the oldest ape-man remains, we certainly have some of the most valuable collections. The rich fruits that we have harvested from Sterkfontein and Swartkrans have had a wonderful and unexpected outcome. It is these uniquely rich hauls of fossil hominids that have been responsible, in the main, for the listing of the dozen sites near Sterkfontein as a World Heritage Site. It was one of the first three South African sites to be so listed on 2nd December 1999. As a South African-born scientist, I look forward to welcoming more South African-born people, especially young students, to work with us, in uncovering the world's most marvellous story. |
Nominations of potential candidates for the Technology Innovation Agency (TIA) Board of Directors
